It is nowadays generally necessary in diesel-powered motor vehicles with automatic transmission to take measures in order to reduce idling vibrations when the automatic transmission is in the “D” (“Drive”) position. This is usually done via a method of control referred to as NI or NIC control (NIC=“neutral idle control”), in which the torque transmission from the converter turbine to the transmission and onwards to the drive shafts is reduced by means of a slipping input clutch. This is also referred to in the case of a six-speed automatic transmission of the so-called “Le Pelletier” type as a C1 clutch. The slipping C1 clutch enables the turbine to rotate at a speed approximately 90 rpm below the idling speed of the internal combustion engine, thereby reducing the converter output torque. The output torque to the axle shafts is then approximately equal to the product of the engine torque and the transmission ratio. This output torque constitutes an external load for the power train, which has to be borne or compensated for by the corresponding response torque of the engine support brackets. These loads acting on the axle shafts and the engine support brackets lead to a high noise level and to the transmission of vibrations into the vehicle interior via the struts and the vehicle body.
Since load reduction by means of the NI method has proved inadequate, a further additional measure taken has been to shift into second gear whilst idling in the “D” drive position of the transmission, thereby further reducing the output torque. Even with this additional measure, however, intrusive idling vibrations are still generated. Although shifting even higher, i.e. into third gear, has also been considered, this may have negative effects on the rollback behavior when negotiating a gradient and can also lead to jerky starting and to a reduction in the service life of the input clutch, since in third gear rapid internal rotations occur in the transmission.
U.S. Pat. No. 7,128,686 B2 discloses a method and a device for the synchronized control of a power-take-off (PTO) unit for supplying winches and lifting appliances, for example, from the power train of a motor vehicle, the transmission drive shaft being locked by an actuation of “internal brakes”, in order to facilitate a clutch engagement between to stationary shafts when the PTO unit is connected.
EP 0 933 562 B1 discloses a control valve system for an automatic transmission, one of the clutches used being situated in the forward gear on the torque input side of one of the transmission elements and a second of the clutches used being situated in the reverse gear on the torque input side of another of the transmission elements, and forward engagement and reverse engagement control valve means being provided, which can be actuated with adjustable pressures via solenoid-actuated valve devices.